It is debatable whether David Sullivan is best known as the owner of Birmingham City or for his porn empire. But the multi-millionaire, whose estimated fortune of £600m put him at number 125 in last year's Sunday Times rich list, has made most of his money from property, with his portfolio estimated to be worth £400m.

He entered the porn market at age 21, selling pornographic pictures, photos and magazines by mail order. By the mid-1970s, he controlled half of the adult magazine market, according to the Sunday Times. He expanded his empire with the help of Ralph and David Gold, who owned the Ann Summers chain of adult stores. It was with the Gold brothers that Sullivan launched the downmarket Sunday Sport newspaper in 1986.

At its peak, sales were 600,000 a week and a daily edition was later launched to capitalise on its success, although sales are a lot lower now.

In 1993, Sullivan, with his old friends the Golds, bought into Birmingham City football club, which was in administration. He was urged into making the purchase by one of his employees, Karen Brady, and he created a stir by appointing her as managing director, making her the first woman on the board of a football league club. She was just 23 at the time.

Last August, it was announced that the mobile adult content group Interactive World was buying the Daily and Sunday Sport in a reverse takeover. Sullivan, who owned a 49.5% stake in Interactive World, announced he was also selling that stake, thus severing his links with the paper.

It came just a month after Sullivan sold 14.81% of his shares in Birmingham City to Hong Kong-based businessman Carson Yeung in July for about £7.5m.As Yeung seemed set on a full takeover, Sullivan announced his intention to cut his ties with the club.

"The honeymoon is long over and we're at the divorce stage now, unfortunately," he told the Guardian in September.

The uncertainty surrounding Yeung's takeover led Birmingham manager Steve Bruce to depart for relegation rivals Wigan in November, amid reports that his position would be in jeopardy under the new regime.

But Yeung failed with his takeover and Sullivan actually increased his stake in the club earlier this year.

From wanting out, Sullivan instead finds himself still co-owner of a club that is under investigation for fraud and in danger of what would be a financially crippling relegation from the Premier league.